I - Transplantation and Associated Cell Membrane Antigens: Human transplantation antigens (HL-A) will be solubilized by several methods, purified, and serologically and biochemically defined. In addition, antigens specific for B cells and for T cells will be isolated by the same techniques as those used to obtain the LH-A antigens. As source material, human lymphoid cells in long-term tissue culture are used. Five cell lines known to possess homozygous HL-A determinants will be used for this study, as well as six cell lines having T or B cell characteristics. These materials, once solubilized, will be assayed by cytotoxic inhibition and by immune precipitation. The biochemical nature of the product obtained will be determined. In addition, attempts will be made to genetically map the B cell specific antigens. II - Acute Leukemia Associated Antigens: Human acute leukemia associated antigens can be identified with serologic techniques employing a complement dependent cytotoxicity assay. A long-term tissue culture cell line, Raji, is known to possess an antigen cross-reactive with the acute leukemia associated antigen. These cells will be used in an immunotherapy protocol in patients with acute lymphocytic leukemia in conjunction with chemotherapy. The immune response of the patient will be monitored using complement dependent cytotoxicity assays against the Raji target cells as well as other acute leukemia cells. Other assays will be migration inhibition and lymphocyte dependent antibody assays. III - Characterization of Lymphocyte Dependent Antibody: Antiserums known to mediate target cell destruction in cooperation with normal lymphocytes have been described. This antibody appears to be different from the complement dependent activity found in many of the same serums. Attempts will be made to separate these antibody activities on a physical basis. In addition, antigenic determinants specific for reactivity with either complement dependent or lymphocyte dependent antibody will be explored.